1. Field of the Invention
The present invention relates generally to microstrip antenna apparatus and more particularly to an improved microstrip antenna array structure in which bent or folded circuit boards are used to significantly increase the surface area available for the integration of circuits and components on a single layer of feed circuit board.
2. Description of the Prior Art
Conventional microstrip printed array antennas employ multiple layer, planar laminated circuit boards to accommodate the multitude of interconnections required to connect discrete active components such as amplifiers and phase shifters to the printed array. The use of such boards requires complex interboard connections, and the size of the discrete active components to be integrated into the array is constrained by the spacing between the array radiating elements. In addition, dissipation of heat in such structures poses a substantial problem.
More specifically, the conventional multiple layer laminated structure consists of multiple layers of circuit boards with patch radiating elements, RF power combining network, control logic circuit, and active components residing on the various layers. The electrical interconnections between boards is usually accomplished by via-holes. The use of multiple layers is necessary because the spacing between the antenna elements, typically on the order of 0.5 to 0.7 wavelengths, is too small to allow sufficient surface area behind each radiating element to accommodate all of the circuitry in one layer. Accordingly, fabrication of such an antenna is usually complex and expensive. Furthermore, it requires a high degree of precision in aligning the various boards which often have different thermal and mechanical properties. Via-hole etching through multiple boards can be used to overcome some of the problems but is very costly and the heat dissipation associated with any active components embedded in the mid-layers is nearly always a problem.